A typical contemporary land vehicle employs a speedometer—a device for displaying the vehicle's instantaneous speed. It is common for a speedometer to receive a signal representing vehicle speed from the vehicle's transmission, if the vehicle is so equipped. In such applications, a transmission output shaft is typically utilized to drive the speedometer.
The speedometer is usually driven either mechanically, via a cable, or electronically, via an electrical wire communicating a frequency of measured electronic pulses corresponding to the rotational speed of the output shaft. Whether driven mechanically or electronically, however, a physical connection is typically required to communicate rotational speed of the output shaft to the speedometer.
Such a physical connection may be subject to various assembly and durability concerns, some of which may result in the speedometer displaying incorrect vehicle speed. Additionally, the speed signal supplied by the transmission and displayed on the speedometer is typically calibrated to correspond to a diameter of wheels originally installed by the vehicle manufacturer. If the manufacturer's wheel rims and tires are subsequently replaced by those having an overall diameter that is different from the factory combination, the speedometer reading may become inaccurate.